Laboratory Diagnosis of Polyomaviruses Infection

D. Laboratory Diagnosis

  1. PML - The clinical diagnosis of PML is confirmed by histological and virological examination of brain material obtained by brain biopsy or at postmortem. Before a biopsy is done, both serum and CSF should be examined for antibodies against JCV. A positive result will not confirm PML, but a negative result makes the diagnosis of PML very unlikely. It is rare to detect antibodies against JC in the CSF. When it is detected, it is suggestive of active multiplication of JCV within the CNS. The brain biopsy or autopsy material can be examined by EM or IEM. The specimen can also be examined directly for JCV antigen by immunofluorescence or immunoperoxidase staining. Virus isolation is very difficult for JCV. When attempted, primary human fetal glial cells are used. The presence of the virus in culture is confirmed by EM, IF or haemagglutination. JC is rarely excreted in the urine of patients suffering form PML.
  2. Renal Tract Infections - the methods generally employed to detect the presence of polyomavirus in urine are cytological examination of the urine for inclusion-bearing cells, EM and virus isolation. The cytology of urine in human polyomavirus infection is quite characteristic. The inclusion-bearing cells have a characteristic appearance and are often present in large numbers. Electron Microscopy of the urinary sediment after centrifugation at 20000 may reveal the presence of polyomavirus particles. It is difficult to isolate JC and BK viruses: Primary PHFG cells must be used for isolation of JCV; BKV have a wider host cell range and HEK cells can be used as well as PHFG cells. More sensitive techniques are being developed, such as dot- blot and PCR.
  3. Serological Diagnosis - HAI is the most widely used serological technique for measuring antibodies against the polyomaviruses. CFT, neutralization, ELISA and RIAs have also been used.

E. Management

Because of the invariably fatal outcome of PML, various antiviral drugs have been tried. The only drug that may have had an effect is cytarabine. Reports have been published on 8 laboratory confirmed cases of PML treated with cytarabine. Long-term improvement was seen in 2 patients. In another person, there was a dramatic response to therapy within 24 hours but this was not maintained. The rapid progression of the disease was halted in a fourth patient but the neurological damage was severe. The remaining 4 individuals did not show any improvement. One should also consider relaxing any immunosuppression regimes in such patients.